In recent years, the use of L-carbohydrates and their nucleoside derivatives in the medicine field greatly increased, and modified nucleosides have shown considerable potential as useful antiviral agents. L-gulose is an important key pentose that constitutes a framework in the synthesis of L-ribonucleosides, L-oligoribonucleosides and many other therapeutic agents. L-nucleosides have high stability against attack of in vivo nucleases or the like, compared to D-nucleosides, and thus are highly potential candidates that can be used as therapeutic agents. As L-gulose is known to be highly useful as a raw material for producing medical drugs such as antiviral agents and antibiotics, it has recently attracted a great deal of attention, and thus it is required to establish a highly efficient biological method for producing L-gulose.
L-gulose is present in small amounts in nature, and the stability and conversion efficiency of enzymes capable of producing L-gulose are low. For this reason, it is difficult to commercialize L-gulose. Thus, in enzymatic production methods of producing L-gulose using biocatalysts, it is required to ensure the stability and high activity of enzymes.